This invention relates in general to systems that monitor parameters in industrial processes for parameter values that are outside of the desired norm, and in particular to systems that monitor pressure vessels for over pressure or under pressure situations, and to equipment that is to be used in connection with devices that automatically shut down a process when an over pressure or under pressure situation could threaten to rupture or collapse the pressure vessel.
Industrial operations, particularly those that include pressure sensitive operations, often require devices that monitor pressure vessels for over pressure or under pressure situations. These monitors are connected to devices which may automatically shut down the industrial process in an over or under pressure situation. One of the problems with these systems is the inability to know if the monitoring system is actually functioning. For example, process materials may clog a sensing port, or otherwise prevent the pressure sensing device from properly monitoring system pressure. In instances where the monitoring system is relied upon to cause the emergency shut down of the process, it is critical that the system either function with 100% reliability, or that the system somehow alert the operator of the facility that it is not working properly, so that it can be repaired. Engineers have improved the reliability of critical shutdown system components in order to improve the level of safety of a production process. However, while the reliability of monitoring systems has improved, they still are not 100% reliable. Furthermore, it would be foolish to assume that a given system is 100% reliable, given the dangerous consequences of vessel failure in an industrial process. Accordingly, it is most important to know when a monitoring system has failed.
The instant invention provides a method and apparatus for monitoring process parameters in a manner that also informs the operator of the status of the monitoring system. Failure of the monitoring system is readily identified, allowing for repair or replacement of the monitoring system, limiting the risk of an un-monitored out of norm parameter value.
The instant invention creates a cycle that is monitored for irregularities in that cycle. A parameter sensing device is connected to a system to be monitored for the value of that parameter. The sensing device is then subjected to an artificially induced value of the parameter being monitored, such that a parameter value set point is reached. The reaching of this set point then triggers the cessation of the artificially induced value of the parameter. The parameter sensing device then returns to its initial statexe2x80x94that of monitoring the value of the parameter in the system to be monitored. However, since the parameter set point is no longer being reached (assuming the value of the parameter in the system being monitored has not reached the set point) this in turn triggers the artificial induction of the value of the parameter. Accordingly, a cycle is created, wherein the parameter value measured by the sensing device reaches the set point of the sensing device, and then returns to a value not reaching the set point. The cycle is disrupted if the equipment that creates the cycle malfunctions in any way, or if the parameter value in the system being monitored has reached the set point. In this manner the invention not only monitors the parameter in the system being monitored, but also continuously checks to insure that the monitoring equipment is functioning properly. Disruptions in the cycle are recognized by a device, such as a computer, that monitors the cycle, and alerts the operator of the system to a potential problem.
A parameter that is often monitored is pressure in pressure vessels. In such an instance the instant invention may utilize a system chamber that is attached to the vessel to be monitored. The pressure in the system chamber is periodically raised using an independent gas source, until a high pressure switch attached to the system chamber is triggered (in an over pressure monitoring situation). This switch then triggers the opening of a solenoid valve, which in turn allows the gas in the system chamber to be released into the vessel being monitored, lowering the pressure in the system chamber. The system chamber may be any convenient size, and may be incorporated into the valve mechanism that connects the instant invention to the vessel to be monitored. When the pressure in the system chamber reaches a level below the set point of the high pressure switch, the solenoid valve is caused to close, which starts the cycle over again.
This pressure cycle in the system chamber is monitored. Changes in the cycle inform the operator of a problem with the monitoring system, or of an over pressure or under pressure situation in the pressure vessel.